Profiling of differentially expressed genes in LRRC4 overexpressed glioblastoma cells by cDNA array

Our previous study has shown that LRRC4 is a novel member of the leucine-rich repeat （LRR） superfamily and has the potential to suppress brain tumor growth. In order to further analyze the functions of LRRC4 on the maintenance of normal function and suppression of tumorigenesis in the central nervous system, we investigated alterations in gene expression related to neurobiology by the Atlas array in two inducible dual-stable LRRC4-overexpressing cell lines. Seventeen of 588 genes spotted on the Atlas membrane showed altered expression levels in LRRC4 transfected U251MG Tet-on cells, which are involved in cell proliferation and cell cycle progression, tumor invasion and metastasis, and neurotransmitter synthesis and release. In addition, cell invasion assay results showed that LRRC4 can inhibit the U251MG cell migration. These studies represent the first cDNA array analysis of the effects of LRRC4 on the involvement of different neurobiological genes in U251MG glioblastoma cells and provide new insights into the function of LRRC4 in glioma.     

Expression and functional characterization of LRRC4, a novel brain-specific member of the LRR superfamily

LRRC4, a novel member of LRR superfamily thought to be involved in development and tumorigenesis of the nervous tissue, has the potential to suppress tumorigenesis and cell proliferation of U251MG cells. This study aimed at revealing the correlation between expression of LRRC4 and the maintenance of normal function and tumorigenesis suppression within the central nervous system. We systematically analyzed the expression and tissue distributions of the gene in tissues. Results showed that LRRC4 expression was limited to normal adult brain, both in human and in mouse, and exhibited a development-regulated pattern, but was down-regulated in brain tumor tissues and U251MG cell line. Furthermore, dynamic alterations in gene expression associated with cell cycle progression were investigated by using Tet-on system. Results showed that LRRC4 induced a cell cycle delay at the late G1 phase, probably through the alteration of the expression of different cell cycle regulating proteins responsible for mediating G1-S progression, such as p21(Waf1/Cip1) and p27(Kip1), Cdk2 and PCNA, p-ERK1/2. These findings suggest that LRRC4 may play an important role in maintaining normal function and suppressing tumorigenesis in the central nervous system.     

LRRC4 inhibits the proliferation of human glioma cells by modulating the expression of STMN1 and microtubule polymerization

LRRC4 is a tumor suppressor of glioma, and it is epigenetically inactivated commonly in glioma. Our previous study has shown that induction of LRRC4 expression inhibits the proliferation of glioma cells. However, little is known about the mechanisms underlying the action of LRRC4 in glioma cells. We employed two-dimensional fluorescence differential gel electrophoresis (2-D DIGE) and MALDI -TOF/TOF-MS/MS to identify 11 differentially expressed proteins, including the significantly down-regulated STMN1 expression in the LRRC4-expressing U251 glioma cells. The levels of STMN1 expression appeared to be positively associated with the pathogenic degrees of human glioma. Furthermore, induction of LRRC4 over-expression inhibited the STMN1 expression and U251 cell proliferation in vitro, and the glioma growth in vivo. In addition, induction of LRRC4 or knockdown of STMN1 expression induced cell cycle arrest in U251 cells, which was associated with modulating the p21, cyclin D1, and cyclin B expression, and the ERK phosphorylation, and inhibiting the CDK5 and cdc2 kinase activities, but increasing the microtubulin polymerization in U251 cells. LRRC4, at least partially by down-regulating the STMN1expression, acts as a major glioma suppressor, induces cell cycle arrest and modulates the dynamic process of microtubulin, leading to the inhibition of glioma cell proliferation and growth. Potentially, modulation of LRRC4 or STMN1 expression may be useful for design of new therapies for the intervention of glioma.     

LRRC4通过LRR结构域抑制脑胶质母细胞瘤U251细胞的生长和侵袭

LRRC4基因是候选的脑胶质瘤抑制基因,其细胞外区域含有一个保守的LRR和一个IgC2 结构域.本研究结合生物信息学分析,通过一步PCR法构建了不同结构域缺失的突变体（pc ΔLRR, pcΔIgC2或pcΔTm）.并将全长LRRC4（pcLRRC4）和各突变体转染至U251细胞,构建了稳定表达的U251细胞系.通过MTT,软琼脂集落形成及Transwell体外侵袭模型检测发现,全长LRRC4能够抑制U251细胞的生长和侵袭;LRR结构域缺失的突变体不再抑制U251细胞的生长和侵袭;而IgC2或Tm区缺失的突变体仍然可以抑制U251细胞的生长和侵袭.该结果表明,LRRC4抑制U251细胞的生长和侵袭依赖于它的LRR结构域,而不是IgC2或Tm结构域.     

Tet 调控的脑相对特异性新基因 LRRC4表达细胞系的构建

LRRC4是一个在脑相对特异性表达的富亮氨酸重复超家族新成员,在神经胶质瘤表达明显下调或缺失且具有抑制脑胶质瘤细胞生长的潜能. 利用 Tet-on 基因表达系统,经过两轮转染,先后将调控质粒 pTet-on 和表达质粒 pTRE-2hyg-LRRC4 转染 U251 细胞系,分别用 G418 和潮霉素 Hygromycin 进行两次筛选. 在第一轮挑取的 80 个克隆中,利用 pTRE-2hyg-luciferase 报告基因进行最佳的低背景高表达的 pTet-on 细胞克隆筛选,在通过量效关系和动力学检测筛选的最佳克隆基础上,再进行 pTRE-2hyg-LRRC4 的转染,并通过 RT-PCR 和 RNA 印迹检测,成功获得了两个具有良好诱导性 Tet 调控的 LRRC4 双稳定表达细胞系,为进一步阐明 LRRC4 在脑胶质瘤发生发展中的作用,提供有利的研究基础和理想的实验平台.     

LRRC4基因转染U251细胞的比较蛋白质组学分析

LRRC4是我室自主克隆的一个脑组织优势表达基因.前期研究结果表明,外源性LRRC4基因转染至U251细胞,可明显地抑制U251细胞的增殖、黏附、趋化和侵袭等生物学行为. 因此,LRRC4亦是一个脑胶质瘤抑制性基因.为了进一步了解LRRC4在胶质瘤发生发展中的调控作用,本研究采用荧光差异凝胶电泳（2D-DIGE）和质谱分析技术获得了LRRC4转染U251细胞的11个差异表达蛋白质,并用Western 印迹证实了U251细胞在转染LRRC4基因前后热休克蛋白27、stathmin 1和S100钙结合蛋白A11的差异表达变化. 这些差异蛋白质涉及细胞代谢、增殖、转录、信号转导等众多事件,表明LRRC4基因转染U251细胞后可能通过调控这些蛋白质的表达而参与细胞的增殖、黏附、趋化和侵袭等生物学过程.     

The influence of simulated microgravity on proliferation and apoptosis in U251 glioma cells

Several studies have indicated that microgravity can influence cellular progression, proliferation, and apoptosis in tumor cell lines. In this study, we observed that simulated microgravity inhibited proliferation and induced apoptosis in U251 malignant glioma (U251MG) cells. Furthermore, expression of the apoptosis-associated proteins, p21 and insulin-like growth factor binding protein-2 (IGFBP-2), was upregulated and downregulated, respectively, following exposure to simulated microgravity. These findings indicate that simulated microgravity inhibits proliferation while inducing apoptosis of U251MG cells. The associated effects appear to be mediated by inhibition of IGFBP-2 expression and stimulation of p21 expression. This suggests that simulated microgravity might represent a promising method to discover new targets for glioma therapeutic strategy.     

LRRC4 inhibits glioblastoma cell proliferation, migration, and angiogenesis by downregulating pleiotropic cytokine expression and responses

Leucine-rich repeat C4 (LRRC4) has been shown to inhibit glioma cell proliferation, however, little is known about the mechanism(s) underlying the action of LRRC4. Here, we show that two glioblstoma U251 cell clones stably expressing LRRC4 were established. LRRC4 expression significantly inhibited the expression of some cytokines and their receptors determined by microarray and Western blot assays, and dramatically reduced cytokine-induced AP-1, NF-kB, and CyclinD1 activation in glioma cells. Furthermore, LRRC4 expression in glioma cells significantly downregulated spontaneous and cytokine-induced expression of K-RAS and phosphorylation of c-Raf, ERK, AKT, NF-kBp65, p70S6K, and PKC, suggesting that LRRC4 inhibited receptor tyrosine kinase (RTK) signaling pathways. Moreover, treatment with bFGF, IGF1, or IGF2 stimulated LRRC4(-/-), but not the LRRC4(+), glioma cell proliferation, indicating that LRRC4 mitigated cytokine-stimulated proliferation in glioma cells. In addition, treatment of LRRC4(-/-) glioma cells with EGF, IGF2, or PDGF promoted long distance mobilization, but induced little migration in LRRC4(+) glioma cells, suggesting that LRRC4 retarded cytokine-promoted glioma cell migration in vitro. Finally, human vessel endothelial cells (ECV304) treated with VEGF grew, aligned and formed hollow tube-like structures in vitro. In contrast, LRRC4(+) ECV304 treated with VEGF failed to form vessel-tube structures. Collectively, LRRC4 expression inhibited the expression of some growth factors, cytokines and their receptors, and the capacity of glioma cells responding to cytokine stimulation, leading to inhibition of glioma cell proliferation. Conceivably, induction of LRRC4 expression may provide new intervention for human glioma in the clinic.     

LRRC4 inhibits human glioblastoma cells proliferation, invasion, and proMMP-2 activation by reducing SDF-1 alpha/CXCR4-mediated ERK1/2 and Akt signaling pathways

Gliomas take a number of different genetic routes in the progression to glioblastoma multiforme, a highly invasive variant that is mostly unresponsive to current therapies. The alpha-chemokine stromal cell-derived factor (SDF)-1 alpha binds to the seven transmembrane G-protein-coupled CXCR-4 receptor and acts to modulate cell migration and proliferation by activating multiple signal transduction pathways. Leucine-rich repeats containing 4 (LRRC4), a putative glioma suppressive gene, inhibits glioblastoma cells tumorigenesis in vivo and cell proliferation and invasion in vitro. We also previously demonstrated that LRRC4 controlled glioblastoma cells proliferation by ERK/AKT/NF-kappa B signaling pathway. In the present study, we demonstrate that CXC chemokine receptor 4 (CXCR4) is expressed in human glioblastoma U251 cell line, and that SDF-1 alpha increases the proliferation, chemotaxis, and invasion in CXCR4+ glioblastoma U251 cells through the activation of ERK1/2 and Akt. The reintroduction of LRRC4 in U251 cells inhibits the expression of CXCR4 and SDF-1 alpha/CXCR4 axis-mediated downstream intracellular pathways such as ERK1/2 and Akt leading to proliferate, chemotactic and invasive effects. Furthermore, we provide evidence for proMMP-2 activation involvement in the SDF-1 alpha/CXCR4 axis-mediated signaling pathway. LRRC4 significantly inhibits proMMP-2 activation by SDF-1 alpha/CXCR4 axis-mediated ERK1/2 and Akt signaling pathway. Collectively, these results suggest a possible important "cross-talk" between LRRC4 and SDF-1 alpha/CXCR4 axis-mediated intracellular pathways that can link signals of cell proliferation, chemotaxis and invasion in glioblastoma, and may represent a new target for development of new therapeutic strategies in glioma.     

Adenovirus-mediated overexpression of p15INK4B inhibits human glioma cell growth, induces replicative senescence, and inhibits telomerase activity similarly to p16INK4A.

The genes encoding the cyclin-dependent kinase inhibitors p16INK4A (CDKN2A) and p15INK4B (CDKN2B) are frequently homozygously deleted in a variety of tumor cell lines and primary tumors, including glioblastomas in which 40-50% of primary tumors display homozygous deletions of these two loci. Although the role of p16 as a tumor suppressor has been well documented, it has remained less well studied whether p15 plays a similar growth-suppressing role. Here, we have used replication-defective recombinant adenoviruses to compare the effects of expressing wild-type p16 and p15 in glioma cell lines. After infection, high levels of p16 and p15 were observed in two human glioma cell lines (U251 MG and U373 MG). Both inhibitors were found in complex with CDK4 and CDK6. Expression of p16 and p15 had indistinguishable effects on U251 MG, which has homozygous deletion of CDKN2A and CDKN2B, but a wild-type retinoblastoma (RB) gene. Cells were growth-arrested, showed no increased apoptosis, and displayed a markedly altered cellular morphology and repression of telomerase activity. Transduced cells became enlarged and flattened and expressed senescence-associated beta-galactosidase, thus fulfilling criteria for replicative senescence. In contrast, the growth and morphology of U373 MG, which expresses p16 and p15 endogenously, but undetectable levels of RB protein, were not affected by exogenous overexpression of either inhibitor. Thus, we conclude that overexpression of p15 has a similar ability to inhibit cell proliferation, to cause replicative senescence, and to inhibit telomerase activity as p16 in glioma cells with an intact RB protein pathway.     

M2 receptor activation inhibits cell cycle progression and survival in human glioblastoma cells

Muscarinic receptors, expressed in several primary and metastatic tumours, appear to be implicated in their growth and propagation. In this work we have demonstrated that M2 muscarinic receptors are expressed in glioblastoma human specimens and in glioblastoma cell lines. Moreover, we have characterized the effects of the M2 agonist arecaidine on cell growth and survival both in two different glioblastoma cell lines (U251MG and U87MG) and in primary cultures obtained from different human biopsies. Cell growth analysis has demonstrated that the M2 agonist arecaidine strongly decreased cell proliferation in both glioma cell lines and primary cultures. This effect was dose and time dependent. FACS analysis has confirmed cell cycle arrest at G1/S and at G2/M phase in U87 cells and U251 respectively. Cell viability analysis has also shown that arecaidine induced severe apoptosis, especially in U251 cells. Chemosensitivity assays have, moreover, shown arecaidine and temozolomide similar effects on glioma cell lines, although IC50 value for arecaidine was significantly lower than temozolomide. In conclusion, we report for the first time that M2 receptor activation has a relevant role in the inhibition of glioma cell growth and survival, suggesting that M2 may be a new interesting therapeutic target to investigate for glioblastoma therapy.     

The role of protein arginine-methyltransferase 1 in gliomagenesis

Protein arginine methyltransferase 1 (PRMT1), a type-I arginine methyltransferase, has been implicated in diverse cellular events. We have focused on the role of PRMT1 in gliomagenesis. In this study, we showed that PRMT1 expression was up-regulated in glioma tissues and cell lines compared with normal brain tissues. The knock-down of PRMT1 resulted in an arrest in the G1-S phase of the cell cycle, proliferation inhibition and apoptosis induction in four glioma cell lines (T98G, U87MG, U251, and A172). Moreover, an in vivo study confirmed that the tumor growth in nude mouse xenografts was significantly decreased in the RNAi-PRMT1 group. Additionally, we found that the level of the asymmetric dimethylated modification of H4R3, a substrate of PRMT1, was higher in glioma cells than in normal brain tissues and decreased after PRMT1 knock-down. Our data suggest a potential role for PRMT1 as a novel biomarker of and therapeutic target in gliomas. [BMB Reports 2012; 45(8): 470-475].     

Combined RNAi-Mediated Suppression of Rictor and EGFR Resulted in Complete Tumor Regression in an Orthotopic Glioblastoma Tumor Model

The PI3K/AKT/mTOR pathway is commonly over activated in glioblastoma (GBM), and Rictor was shown to be an important regulator downstream of this pathway. EGFR overexpression is also frequently found in GBM tumors, and both EGFR and Rictor are associated with increased proliferation, invasion, metastasis and poor prognosis. This research evaluated in vitro and in vivo whether the combined silencing of EGFR and Rictor would result in therapeutic benefits. The therapeutic potential of targeting these proteins in combination with conventional agents with proven activity in GBM patients was also assessed. In vitro validation studies were carried out using siRNA-based gene silencing methods in a panel of three commercially available human GBM cell lines, including two PTEN mutant lines (U251MG and U118MG) and one PTEN-wild type line (LN229). The impact of EGFR and/or Rictor silencing on cell migration and sensitivity to chemotherapeutic drugs in vitro was determined. In vivo validation of these studies was focused on EGFR and/or Rictor silencing achieved using doxycycline-inducible shRNA-expressing U251MG cells implanted orthotopically in Rag2M mice brains. Target silencing, tumor size and tumor cell proliferation were assessed by quantification of immunohistofluorescence-stained markers. siRNA-mediated silencing of EGFR and Rictor reduced U251MG cell migration and increased sensitivity of the cells to irinotecan, temozolomide and vincristine. In LN229, co-silencing of EGFR and Rictor resulted in reduced cell migration, and increased sensitivity to vincristine and temozolomide. In U118MG, silencing of Rictor alone was sufficient to increase this line’s sensitivity to vincristine and temozolomide. In vivo, while the silencing of EGFR or Rictor alone had no significant effect on U251MG tumor growth, silencing of EGFR and Rictor together resulted in a complete eradication of tumors. These data suggest that the combined silencing of EGFR and Rictor should be an effective means of treating GBM.     

Phorbol 12-myristate 13-acetate induces protein kinase ceta-specific proliferative response in astrocytic tumor cells

Protein kinase C (PKC) activation has been implicated in cellular proliferation in neoplastic astrocytes. The roles for specific PKC isozymes in regulating this glial response, however, are not well understood. The aim of this study was to characterize the expression of PKC isozymes and the role of PKC-eta expression in regulating cellular proliferation in two well characterized astrocytic tumor cell lines (U-1242 MG and U-251 MG) with different properties of growth in cell culture. Both cell lines expressed an array of conventional (alpha, betaI, betaII, and gamma) and novel (theta and epsilon) PKC isozymes that can be activated by phorbol myristate acetate (PMA). Another novel PKC isozyme, PKC-eta, was only expressed by U-251 MG cells. In contrast, PKC-delta was readily detected in U-1242 MG cells but was present only at low levels in U-251 MG cells. PMA (100 nm) treatment for 24 h increased cell proliferation by over 2-fold in the U-251 MG cells, whereas it decreased the mitogenic response in the U-1242 MG cells by over 90%. When PKC-eta was stably transfected into U-1242 MG cells, PMA increased cell proliferation by 2.2-fold, similar to the response of U-251 MG cells. The cell proliferation induced by PMA in both the U-251 MG and U-1242-PKC-eta cells was blocked by the PKC inhibitor bisindolylmaleimide (0.5 micrometer) and the MEK inhibitor, PD 98059 (50 micrometer). Transient transfection of wild type U-251 with PKC-eta antisense oligonucleotide (1 micrometer) also blocked the PMA-induced increase in [(3)H]thymidine incorporation. The data demonstrate that two glioblastoma lines, with functionally distinct proliferative responses to PMA, express different novel PKC isozymes and that the differential expression of PKC-eta plays a determining role in the different proliferative capacity.     

Saponin 1 Induces Apoptosis and Suppresses NF-κB-Mediated Survival Signaling in Glioblastoma Multiforme (GBM)

Saponin 1 is a triterpeniod saponin extracted from Anemone taipaiensis, a traditional Chinese medicine against rheumatism and phlebitis. It has also been shown to exhibit significant anti-tumor activity against human leukemia (HL-60 cells) and human hepatocellular carcinoma (Hep-G2 cells). Herein we investigated the effect of saponin 1 in human glioblastoma multiforme (GBM) U251MG and U87MG cells. Saponin 1 induced significant growth inhibition in both glioblastoma cell lines, with a 50% inhibitory concentration at 24 h of 7.4 µg/ml in U251MG cells and 8.6 µg/ml in U87MG cells, respectively. Nuclear fluorescent staining and electron microscopy showed that saponin 1 caused characteristic apoptotic morphological changes in the GBM cell lines. Saponin 1-induced apoptosis was also verified by DNA ladder electrophoresis and flow cytometry. Additionally, immunocytochemistry and western blotting analyses revealed a time-dependent decrease in the expression and nuclear location of NF-κB following saponin 1 treatment. Western blotting data indicated a significant decreased expression of inhibitors of apoptosis (IAP) family members,(e.g., survivin and XIAP) by saponin 1. Moreover, saponin 1 caused a decrease in the Bcl-2/Bax ratio and initiated apoptosis by activating caspase-9 and caspase-3 in the GBM cell lines. These findings indicate that saponin 1 inhibits cell growth of GBM cells at least partially by inducing apoptosis and inhibiting survival signaling mediated by NF-κB. In addition, in vivo study also demonstrated an obvious inhibition of saponin 1 treatment on the tumor growth of U251MG and U87MG cells-produced xenograft tumors in nude mice. Given the minimal toxicities of saponin 1 in non-neoplastic astrocytes, our results suggest that saponin 1 exhibits significant in vitro and in vivo anti-tumor efficacy and merits further investigation as a potential therapeutic agent for GBM.     

LRRC4融合蛋白的构建与表达研究

在前期工作中,采用EST介导的定位候选克隆策略,克隆了一个在脑瘤中表达下调的脑特异表达新基因LRRC4,为进一步研究其结构与功能的关系,构建了含LRRC4基因全长编码区的pGEM-T Easy质粒,在此基础上通过亚克隆构建了LRRC4融合蛋白的绿色荧光蛋白（pEGFP-C1）表达质粒,瞬时转染哺乳动物细胞,结果发现表达的LRRC4融合蛋白定位于活细胞的细胞膜上.同时,构建了LRRC4全长和截短型原核表达pGEX-4T-2质粒,成功而高效地在大肠杆菌BL21 中表达LRRC4融合蛋白.上述工作为制备多抗,深入研究LRRC4基因的功能奠定了基础.